Septic shock (also known as sepsis) causes more than 150,000 deaths annually in the United States. Sepsis is defined as a clinical disorder whose symptoms may include well defined abnormalities in body temperature, heart rate, breathing rate, white blood cell count, hypotension, organ perfusion abnormalities, and multiple organ dysfunction. It may be caused by bacterial (either gram negative or gram positive), fungal, viral and other infections as well as by non-infective stimuli such as multiple trauma, severe burns, organ transplantation and pancreatitis. In Europe there are 500,000 cases annually with a lethal outcome of 40-70%. Even with improved patient management the mortality rate ranges from 50% to 75% in patients with established septic shock. There has not been a significant decrease in this mortality rate since the advent of broad spectrum antibiotics in the early 1960s. Septic patients usually die as a result of poor tissue perfusion and injury followed by multiple organ failure. It is now generally accepted that a significant portion of the peripheral responses occurring during septic shock are initiated by endotoxin. Endotoxin (also referred to herein as lipopolysaccharide, bacterial lipopolysaccharide or LPS), an outer membrane component of gram-negative bacteria, is released upon the death or multiplication of the bacteria. Administration of endotoxin to experimental animals elicits a series of sequential cardiovascular, metabolic, and pathologic responses culminating in organ dysfunction and failure, ultimately resulting in death. When endotoxin is administered to normal human subjects, physiologic, biochemical, and cellular responses are induced that quantitatively mimic those occurring during septic shock. However, it is becoming increasingly recognized that the majority of responses observed during sepsis and endotoxemia are not due to direct actions of endotoxin, but result from endotoxin induction of a myriad of cellular and humoral inflammatory mediators. Furthermore, even with the vast research and clinical literature regarding sepsis and endotoxemia, there is no definitive regimen for the treatment of septic shock with the thrust of therapy being targeted at correction of symptoms.
Clinicians are dissatisfied with the existing therapies for septic shock which currently consist of antibiotic therapy or hemodynamic and metabolic support. The intravenous antibiotics eradicate the bacteria and the fluid infusion attempts to reverse the hypotension.
The impact of sepsis and any situation of endotoxemia is particularly devastating to patients with compromised cardiac and hepatic function and to immunocompromised patients. Patients at high risk are the elderly (an increasing percentage of our society), chemotherapy patients, and those requiring surgery or invasive instrumentation. The current therapy of antibiotics and hemodynamic support has not proven to be successful. Experimental studies have indicated that antibodies to certain cytokines may ameliorate some, but not all of the manifestations of the sepsis syndrome. There is such an explosion of physiological responses and release of mediators during septic shock that the antagonism of a single mediator may not always be effective.
Although septic shock can follow any bacterial infection, it is most often the sequel to a gram negative infection. Klebsiella, Pseudomonas, Escherichia coli, Bacteroides and Salmonella are the most frequent cause.
Septic shock usually begins with tremor, fever, falling blood pressure, rapid breathing and heart beat, and skin lesions. Within hours or days it can progress to spontaneous clotting in the blood vessels, severe hypotension, multiple organ failure and death.
Most of the damage comes not from the invading bacteria but from endotoxin. The component responsible for the toxic effect of the LPS molecule is the lipid component, called lipid A. This region is buried in the outer membrane of the bacterium and is believed to be reasonably constant between different species of gram negative bacteria. The polysaccharide region of the molecule extends from the surface of the bacterium and is different for each bacterial strain. The polysaccharide region consists of an inner core region composed of a heptose, and a 3, deoxy-D-manno-2-octulosonic acid (KDO) molecule. The KDO molecule is found in all lipopolysaccharide and links the polysaccharide to the lipid A moiety.
The manner in which endotoxin evokes its effects is by binding to cells such as monocytes/macrophages or endothelial cells, and triggering them to produce various mediator molecules such as toxic oxygen radicals, hydrogen peroxide, tumor necrosis factor-alpha (TNF-.alpha.), various interleukins (IL-1, IL-6, and IL-8). Endotoxin in even the very smallest amounts can activate these cells.
Depending on the dose or concentration of endotoxin, the effects may either be deleterious or advantageous to the host. If excessive TNF-.alpha., IL-1, IL-6, and IL-8 are produced, they can evoke endotoxic (or septic) shock with symptoms ranging from chills and fever to circulatory failure, multiorgan failure, and death. An improved method of treating or preventing septic shock would be of great value.